Cumene is an important intermediate in the chemical and polymer industries, with global cumene production currently exceeding twelve million metric tons annually. The majority of all cumene manufactured in the world today is used for the production of phenol. The demand for phenol for the manufacture of Bisphenol-A and subsequently polycarbonates is accelerating, owing to the broadening application of polycarbonates in the electronic, healthcare, and automobile industries.
Commercial production of cumene generally involves the reaction of benzene with propylene under liquid phase or mixed gas-liquid phase conditions in the presence of an acid catalyst, particularly a zeolite catalyst. However, the demand for, and hence the cost of, propylene is increasing. There is therefore interest in developing alternative methods of producing cumene in which the propylene is replaced or supplemented by alternative C3 alkylating agents. For example, U.S. Pat. No. 5,015,786 discloses a process in which acetone from a phenol plant is hydrogenated to produce isopropanol and the resultant isopropanol is then used as a C3 alkylating agent in the liquid phase alkylation of benzene to cumene. This process has the added advantage that the production of phenol from cumene generates an equimolar amount of acetone, whereas the phenol and acetone are used at an approximately 2:1 molar ratio to produce Bisphenol-A. Thus, the process provides an attractive method of converting the excess acetone from phenol production to generation of the more advantaged product of cumene.
Isopropanol is not only useful as an alkylating agent for the production of cumene, but also enjoys wide application as a solvent, a gasoline additive and in various medical and pharmaceutical applications. On a commercial scale, isopropanol is produced either by acetone hydrogenation or via the direct or indirect hydration of propylene. However, each of these processes produces a crude isopropanol product containing significant quantities of water, whereas a key specification for industrial grade isopropanol is a water level of no more than 0.1 wt %. Removal of the water from the crude isopropanol product can be accomplished by fractionation or stripping, in conventional distillation systems, where water is removed as a light product and isopropanol product is produced as a heavy product with reduced water content. However, since water and isopropanol form a minimum boiling homogeneous azeotrope with a composition of approximately 80 wt % isopropanol and 20 wt % water, the initial water removal step results in an inevitable yield loss of isopropanol. Additional measures can be taken to reduce the isopropanol loss, such as the use of agents that either break the azeotrope, for example acetone, or form another azeotrope with water, such as benzene, or the use of solids adsorbents or selective membranes. However, all of these measures require additional equipment and processing steps, increasing the capital expenditure and operating cost, and hence increasing the cost to purify the isopropanol.
In accordance with the present invention, it has now been found that, by integrating the purification of isopropanol with a process for producing cumene from acetone, the purification of the crude isopropanol product can be simplified, thereby reducing production costs.